The present invention relates to an improvement in the type of electrical switch generally known as a "dome" switch.
The configurations of various dome switches as now used in the art are exemplified in U.S. Pat. Nos. 4,074,088; 4,042,439; and 3,653,038. Such switches employ a central point contact circumscribed by a circular or nearly circular contact. In many cases, the circular contact is physically, but not electrically, discontinuous. A resilient, electrically conductive dome rests on its edges on the circular contact, and overlies and is spaced from the central contact. The switch is actuated by pressing the center of the dome into physical contact with the central contact to establish an electrical connection between this contact and the circular contact and thereby close the switch.
Dome switches are used in a variety of applications, usually those in which a plurality of relatively inexpensive switches are required. In such applications, the switches can be either mechanically actuated by some device, or manually actuated by the user. An example of a mechanically actuated dome switch is found in video games in which the dome switches are actuated by studs orthogonally disposed about the axis of a controlling joy stick. Manually actuated dome switches are often employed in keyboards for small hand-held calculators.
The principal advantages of the dome switch lies in the simplicity of the parts necessary to construct the switch, and the ease with which the switch can be assembled, particularly as part of an automated assembly process. The dome switch is ideally suited for use in high volume, mass produced, cost competitive items in which several switches must be employed.
A problem which has hampered the use of dome switches in the past is that the life of the switch is very difficult to predict, and such switches are subject to random premature failure. It has been found that when a simple dome switch as described above is employed, the edges or support points of the dome dig into the circular contact when the dome is depressed and released to actuate and deactuate and switch. Such movement can cause premature wear of the anti-oxidation overplating on the second contact, and the switch is subject to unexpected and unpredictable failure at any time. Since such switches are often integral to a complex mechanism involving many parts, failure of the relatively inexpensive dome switch generally requires replacement of the entire mechanism.